Migration Mechanisms of POE Surfaces in Injection Molding iPP/POE Blends
The driving force and factors affecting the migration of ethylene-octene copolymer(POE)phase onto the surface of isotactic polypropylene(iPP)/ethylene-octene copolymer(POE)blends remain unclear.Thus,injection molding samples of iPP and POE8137 blends with four relative molecular weights were studied.The migration behaviors and influencing factors of POE during annealing at 150℃were investigated by employing the morphological characterization techniques such as scanning electron microscopy,atomic force microscopy,and the crystallographic structural characterization techniques such as wide-angle X ray diffraction and small-angle X ray scattering,as well as the dynamic mechanical analyses.The results show that the degree of POE migration during short-time high-temperature annealing is significantly related to the molecular weight of the matrix resin iPP.The degree of POE migration after annealing is higher when the molecular weight of iPP increases.It is speculated that the migration mechanism of POE is caused by a surface segregation effect,which is similar to that in amorphous blend film systems.Annealing for 0-4 h,iPP undergoes structural reconstruction,resulting to an increase in crystallinity,the average thickness of the amorphous region,and the mobilty of the molecular chains in the amorphous region.These factors promote the POE migration.After annealing for 4 h,the reconstruction of iPP crystal structure is completed,while the migration of POE still continues,which further illustrates that the migration mechanism of POE is the surface segregation effect.
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